1. Field of the Invention
The present invention relates to a transmission control unit for use in the transmission and reception of data between portable electronic devices such as portable word processors and lap-top personal computers over a public telephone.
Conventionally, there is a known electronic device having a modulator/demodulator (MODEM) or an acoustic coupler for the purpose of transmitting and/or receiving data to and from an electronic device on the other end of the line.
FIG. 5 is a structural view of an electronic device including a MODEM, the electronic device 50 of this type being used in such a manner that a MODEM 51 thereof is directly connected to a telephone line 52 so as to call an electronic device on the other end of the line by using a tone dial. FIG. 6 is a structural view of an electronic device including an acoustic coupler, where a microphone 62 and a speaker 63 are installed therein via a MODEM 61 so that a connection with a telephone line 52 is established by dialing a call with the microphone 62 and the speaker 63 caused to confront a speaker 64 and a microphone 65 of a telephone 66.
There is a requirement that the electronic device including the MODEM usually directly connected to the telephone line can be connected to the telephone line over a public telephone or the like in the place where the user is.
However, the electronic device 50 of the type shown in FIG. 5 is not designed to be used via a public telephone so that it is impossible to connect the electronic device 50 to the telephone line via the public telephone. In the case of the electronic device 60 of the type shown in FIG. 6, it cannot be used while connected directly to the telephone line 52. Furthermore, the electronic device 60 encounters a problem in that the dial must be turned when it is connected to the telephone line 52 via a public telephone.
In Japanese Utility Model Laid-Open No. 64-11046, a telephone which also serves as an acoustic coupler is disclosed. In this telephone, an acoustic coupler and a telephone unit are mounted on a base in such a manner that a transmitter and a receiver of the acoustic coupler can swing on the base so that the transmitter and the receiver are caused to confront the handset of the telephone. Furthermore, a belt is provided for the base for the purpose of fixing the transmitter and the receiver to the handset of the telephone. When the telephone which also serves as an acoustic coupler is used to communicate with, for example, a portable facsimile, the structure of the facsimile device can be simplified since a telephone which also serves as an acoustic coupler can be connected to the facsimile as an alternative to separately connecting the acoustic coupler and the telephone. However, since the acoustic coupler and the telephone are mounted on the base, it is not suitable to be used via a public telephone. Furthermore, dialing must be conducted by pressing the push buttons when the telephone which also serves as an acoustic coupler is connected to the telephone line.